利用計算流體力學模擬氮化鎵2維/3維 之金屬有機化學氣相沉積產物

Abstract

本文以計算流體力學 (CFD) 數值方法分析垂直式金屬有機氣相沉積（MOCVD）爐內氮化鎵 (GaN) 磊晶沈積速率的各種因素。利用計算流體力學分析在2維熱流場找尋其穩定狀態，並分別比較不同金屬薄膜厚度與基板間隙對於基板表面速度與溫度分佈的影響。此外，亦比較與不同轉速與不同腔體高度對於基板表面速度與溫度分佈的影響。透過本文參數設定可以發現在流量30,000 sccm、溫度1323 K與轉速800 rpm固定下，壓力在100 Torr流場為穩定狀態。另一方面，經由不同腔體高度 (16mm至31mm) 的探討即可發現Gr/Re2浮力與慣性量比皆小於0.5，溫度場則呈現穩定狀態且其溫度差異為0.5 K。 加入化學反應之3維模擬，針對三醇化鎵（TMG）、氮氣 (N2) 和氨氣 (ammonia) 等三種氣體進行氣流場模擬。經由本文討論，可發現在定量30,000 sccm下，轉盤速度調整愈高其非均勻性越高且沉積速率也愈高，而100 rpm 與 1600rpm 之沉積速度最大可相差至兩倍。針對非均勻性來討論，除了轉速100 rpm非均勻性高達16%，其它轉速 (400-1600rpm) 之非均勻性皆在5%以內。入口流量(7,500-90,000sccm) 調整將造成轉盤動量與入口慣性動量比的差異；針對本文所討論之幾何圖形，可得知在轉盤速度固定800 rpm下，其Gr/RewRe值在0.032至0.008範圍內其非均勻性皆可維持至在5%以內。

Metal organic chemical vapor deposition (MOCVD) process of GaN in the vertical reactor is studied by various computational fluid dynamics (CFD) simulations under 2D condition. First, with different pressure, figuring out that flow distribution at 100 Torr is stable. Second, we use CFD to analyze temperature distribution inside gap between wafer carrier and substrate, then adding metal film below substrate to process with different temperature. Third, discussing flow distribution stability on substrate with different rotation speed (100rpm-800rpm). Meanwhile, comparing flow influence for temperature at different height from inlet to substrate (16mm–31mm). Trough simulation, if Gr/Re2 number is below 0.5 under 100 Torr, 800 rpm, 1323K and 30,000 sccm condition, the flow distribution is stable. Finally, temperature difference for different height is 0.5K. After 2D simulation, I use 3D CFD simulations implement gas phase chemical reactions and surface chemical reactions for GaN growth from trimethylgallium, nitrogen and ammonia. By fixing condition of total flow rate 30,000 sccm, high speed rotation causes high nonuniformity and high growth rate. Growth Rates for 1,600 rpm rotation plane is twice than 100 rpm. With nonuniformity viewpoint, between 400 rpm and 1,500 rpm plane decreases below 5%. However, low rotation speed as 100 rpm will cause 16% high nonuniformity due to buoyancy influence. On the other hand, through study of flow rate control (7,500sccm–90,000sccm), it will cause different flow distribution and nonuniformity. Especially for ratio of buoyancy influence to plane inertia of momentum and inlet inertia of momentum (Gr/RewRe) discussion, high Gr/RewRe (0.64) will form Rotation–induced flow or vorticity on substrate. As a result, vorticity will caused 6%。In other word, low (Gr/RewRe) between 0.032 to 0.008 will keep stability flow distribution and control below 5%.